Dr Ingrid Romijn
- Si-PV Manufacturing Technology
- Bifacial solar cells and modules
With double sided (bifacial) PV we can increase electricity generated by solar panels with 10% to 30%. This has the potential to reduce the costs of electricity tremendously. For instance, PV installations or projects can produce the same amount of power on A reduced area and with fewer PV modules and system components.
To accurately predict the energy that will be generated by a PV system consisting of bifacial modules for any partner, ECN part of TNO has developed a very advanced - and to our knowledge the most complete - PV system simulation model, called BIGEYE. With BIGEYE, PV systems of any configuration, at any location on earth can be simulated. This includes systems on rooftops, in large field applications, panels integrated in noise barriers, on water and for instance in tracking systems where the panels follow the trajectory of the sun throughout the day. Using weather and environmental data, the electricity produced can be calculated on an hourly, daily, monthly or yearly basis.
For PV installers, project developers and systems owners it will be of great value to know the electricity generation profile accurately in order to provide optimal connections to the local, national or global electricity grid. Furthermore, BIGEYE can be used to design PV systems in such a way that the generated power better matches the daily need, for instance by increasing generation in mornings or afternoons.
A bifacial PV panel consists of 60 or 72 bifacial solar cells. These cells have an almost identical metal grid on the front and rear side, which leaves more than 95% of both areas open to catch the light. Bifacial panels are installed in regular PV power plants, but also in upcoming market segments such as infrastructure integrated PV, for example noise barriers and so-called floated PV on open water or dual-use hydro- or aquaculture farms.
ECN part of TNO develops knowledge and technology for bifacial PV on cell, module and system level.
We are working on several new cell concepts that aim to increase the conversion efficiency while also reducing the manufacturing costs. One of our novel bifacial solar cell concepts is the PERPoly solar cell. This cell has special interface layers on the rear side, i.e. very thin oxide and polysilicon, which reduce the loss of the electrons that are generated by the light. This way, the efficiency of the cells can increased significantly, potentially up to 25%.
This cell concept has been developed together with Tempress Systems, Levitech B.V., Meyer Burger BV., TU Eindhoven, TU Delft and the University of Twente in a TKI Urban Energy subsidy project as well as in some commercial projects. It is now ready for industrial implementation cross section of ECNs polysilicon based passivating contact solar cell.
ECN part of TNO designs and develops bifacial modules to comply with specific requests: for instance reduced silver consumption to optimize cost and performance under lower light conditions, the use of various light trapping materials to improve light coupling in and on the modules, and solutions for cell and bypass diode positioning to account for increased shading due to robust frames, e.g., in solar noise barriers. ECN part of TNO has also developed a novel bifacial solar panel design with a white layer between and around the cells. These white bifacial solar panels show a 5% increase in energy yield compared to bifacial panels with a glass back and show the same maximum power output as a monofacial panel. The increased yield of white bifacial panels compared to monofacial panels depends on the location of the installation and can be as high as 15 to 35%.
Standard monofacial solar panels can only harvest light with their front side. Double-sided, or bifacial solar panels can also capture light that falls on the rear side of the panel and convert this into electricity. This way, also scattered and diffuse light on the back of the panels can be used. For example, light that reflects from the surface on which the panel is installed will be transmitted through the transparent rear foil or glass of the panel into the bifacial solar cells inside the panel.